Development of Gas Electron Multiplier Detectors for Muon Tomography M. Abercrombie, A. Quintero, A. Menendez, K. Gnanvo, M. Hohlmann Physics and Space Science Department Florida Institute of Technology M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Overview Why GEMs? How GEMs work Assembly process Improvements M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Why GEMs? Compact design, versatile Better spatial resolution than similar techniques (50-100 µm) Relatively low cost Uses naturally occurring, ubiquitous cosmic ray muons, easily penetrate high z materials Well suited for muon tomography of potential nuclear contraband. My talk today is going to be about using GEM detectors for muon tomography as a means for detecting shielded nuclear contraband…Muons easily penetrate, good for detection high z materials M. Abercrombie - Florida Academy of Sciences - March 19, 2010

GEM Foils GEM foils are made of a thin sheet of Kapton covered on both sides by copper High density of tiny, chemically etched holes (~100 per mm2) Foils stretched, framed, and glued; delicate and tedious process When stretching must ensure uniformity. M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Testing the Foils Cleanroom N2 gas flow Voltage of 500V applied Expect a leakage current of less than 5nA 5 volume exchanges in 3 hours. Conducted in our Class 10,000 cleanroom. Causes of leakage current (to be too high), want to ensure that sparking doesn’t occur (why?) Apply voltage using _____? Image taken at CERN M. Abercrombie - Florida Academy of Sciences - March 19, 2010

How GEMs Work Multiple foils stacked inside the detector Sealed and put under Ar/CO2 gas mixture Voltage applied to the foils creates a uniform electric field between foils Why do we use 3? What the Ar/Co2 does. Important that the foils are flat and precisely spaced so that the correct electric field is present. Explain the pictures! M. Abercrombie - Florida Academy of Sciences - March 19, 2010

How GEMs Work Muon ionizes the Ar/CO2 gas in the detector Electrons from ionization process move toward the readout plane Accelerated by high electric field, excites more electrons Cascade of electrons Readout in 2 dimensions What are the electric fields, and why are they those particular values? M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Our Set Up at Florida Tech High voltage supply, HV circuit board, 10 x 10 cm detector, oscilloscope, preamp, gas flow. What does the HV Circuit board do? HV Power Supply HV Circuit Board 10 cm x 10 cm detector Preamp Oscilloscope Gas Flow M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Our Set Up at CERN Prototype for a Muon Tomography station determine incoming and outgoing paths angle of deflection gives target composition Four 30 cm x 30 cm GEM detectors 3 cm x 3 cm x 3 cm target M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Results from CERN: Gain Curve Gain defined as ratio of collected charges at readout to primary charge Logarithmic behavior The gain in GEM detectors depends on geometry of the holes, external fields and gas mixture. The gain of the detectors is defined as ratio of collected charges with the readout to primary charge, this is done measuring the collected current at a known radiation flux. A logarithmic behavior with a gas gain up to 2  104 was obtained as expected. Used a 8.04 keV collimated X-ray generator and GDD-CERN’s lab electronic to calculate the gain of one of the six detectors made. M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Results from CERN: Uniformity Test Test for consistent readout across the detector Position (cm) Average Peak (ADC) 1 (0) 1434 2 (4) 1395 3 (7.8) 1341.5 4 (11.6) 1342 5 (15.5) 1566 6 (19.5) 1498 7 (21.1) 1384 Total Average 1422.929 Stan Dev. 83.36987 7 6 5 4 3 2 1 M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Results from CERN: Spectra Energy spectrum of Cu X-rays in blue Cosmic ray muon pulse height distribution in red (5 hours) M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Improvements Goal: Avoid tedious framing procedure How: Use honeycomb spacers between the foils will ensure that the GEM foils are flat will not require that the foils be framed Would be a significant improvement in the construction of GEM detectors. What are the honeycomb spacers made out of? M. Abercrombie - Florida Academy of Sciences - March 19, 2010

Future Work Obtain a signal with our 10 cm x 10 cm detector Test the performance of honeycomb spacers between foils Construction of a 30 cm x 30 cm detector with honeycomb spacers Learn more at: http://research.fit.edu/hep_labA/ M. Abercrombie - Florida Academy of Sciences - March 19, 2010